1.4- fran -Dimethylcyclohexane

Common Name 1,4-frans-Dimethylcyclohexane Synonym trans-1,4-dimethylcyclohexane Chemical Name 1,4-fran -dimethylcyclohexane CAS Registry No 2207-04-7 Molecular Formula C8H16 Molecular Weight 112.213 Melting Point (°C) ... 

It is clear that this representation of c/5 -dimethyl-cyclohexane shows a plane of symmetry, and we can deduce it to be a meso compound. No such plane of symmetry is present in the representation of fran -dimethylcyclohexane. Why does this approach work Simply because the transformation of planar cyclohexane (with echpsed bonds) into a non-planar form (with staggered bonds) is a conformational change achieved by rotation about single bonds. The fact that cyclohexane is non-planar means we may have to invoke the conformational mobihty to get the three-dimensional picture. 

This dry ozonation procedure is a general method for hydrox-ylation of tertiary carbon atoms in saturated compounds (Table 1). The substitution reaction occurs with predominant retention of configuration. Thus cis-decalin gives the cis-l-decalol, whereas cis- and frans-l,4-dimethylcyclohexane afford cis- and trans-1,4-dimethylcyclohexanol, respectively. The amount of epimeric alcohol formed in these ozonation reactions is usually less than 1%. The tertiary alcohols may be further oxidized to diols by repeating the ozonation however, the yields in these reactions are poorer. For instance, 1-adamantanol is oxidized to 1,3-adamantane-diol in 43% yield. Secondary alcohols are converted to the corresponding ketone. This method has been employed for the hydroxylation of tertiary positions in saturated acetates and bromides. 

This type of reasoning may be applied to other dimethylcyclohexanes, as indicated in the figure. There is no easy way to predict the result it must be deduced in each case. One conformer is of much lower energy in the cases of trans-1,2-, cis-1,3-, and fran -l,4-dimethylcyclohexane both conformers have equal energy in the cases of cis-1,2-, trans-1,3-, and CM-1,4-dimethyIcyclohexane. 

Figure 4.16 Conformations of frans-1,2-dimethylcyclohexane. The conformation with both methyl groups equatorial is favored by 11.4 kJ/mol (2.7 kcal/mol) over the conformation with both methyl groups axial.

Sampl ProbiGm 4.4 Draw both chair conformations for frans-1,3-dimethylcyclohexane. 

The stable chair-chair conformation of gauche interactions compared to one in the chair form of frans-1,2-dimethyl-cyclohexane and three in the chair conformations of cis-decalin and cis-l,2-dimethylcyclohexane. The various factors affecting cis-trans equilibrium of the decalins are given in Table III. Both isomers have an... 

WeTl begin with cis- and fran.y-l,4-dimethylcyclohexane. A conventional method to represent cis and trans stereoisomers in cyclic systems nses wedge-and-dash descriptions as shown. 

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